A Beginner’s Guide to System.Security.SecurityRules and SecuritySafeCritical in C#


In the .NET Framework, security is a critical concern. Two attributes, System.Security.SecurityRules and SecuritySafeCritical, play a significant role in enforcing Code Access Security (CAS).


The System.Security.SecurityRules attribute specifies the set of security rules that the common language runtime should enforce for an assembly. It has two levels: Level1 and Level2.


Level1 uses the .NET Framework version 2.0 transparency rules. Here are the key rules for Level1:

  • Public security-critical types and members are treated as security-safe-critical outside the assembly.
  • Security-critical types and members must perform a link demand for full trust to enforce security-critical behavior when they are accessed by external callers.
  • Level1 rules should be used only for compatibility, such as for .NET Framework 2.0 assemblies.

[assembly: System.Security.SecurityRules(System.Security.SecurityRuleSet.Level1)]
public class MyClass
    // Your code here


The SecuritySafeCritical attribute identifies types or members as security-critical and safely accessible by transparent code. Code marked with SecuritySafeCritical must undergo a rigorous security audit to ensure that it can be used safely in a secure execution environment. It must validate the permissions of callers to determine whether they have authority to access protected resources used by the code.

public void MyMethod()
    // Your code here

Relationship between System.Security.SecurityRules and SecuritySafeCritical

The System.Security.SecurityRules and SecuritySafeCritical attributes work together to enforce security in .NET Framework. An assembly marked with SecurityRules(SecurityRuleSet.Level1) uses the .NET Framework version 2.0 transparency rules, where public security-critical types and members are treated as security-safe-critical outside the assembly.

The concept of trusted Code

Trusted code refers to code that has been granted certain permissions and is considered safe to execute. It’s a combination of techniques, policies, and procedures for which there is no plausible scenario in which a document retrieved from or reproduced by the system could differ substantially from the document that is originally stored. In other words, trusted code certifies that electronically stored information (ESI) is an authentic copy of the original document or information.

Use Cases and Examples

Consider a scenario where you have a method that performs a critical operation, such as accessing a protected resource. You want to ensure that this method can only be called by trusted code. You can mark this method as SecuritySafeCritical to enforce this.

public void AccessProtectedResource()
    // Code to access protected resource

In this case, the AccessProtectedResource method can only be called by code that has been granted the necessary permissions. This helps to prevent unauthorized access to the protected resource.


Understanding the System.Security.SecurityRules and SecuritySafeCritical attributes is crucial when developing secure .NET applications. By using these attributes correctly, you can enforce robust security rules and protect your application from potential threats. Always remember, with great power comes great responsibility!

I hope this article helps you understand these concepts better. Happy coding! 😊